makurdi ferrosilicon ferrosilicon crushing production line

brief introduction of ferrosilicon mill
-china henan zhengzhou mining machinery co.,ltd

brief introduction of ferrosilicon mill -china henan zhengzhou mining machinery co.,ltd

Ferrosilicon mill has the advantage of compact structure, small area needed, easy installation, good ground partical size, low energy consumption, low noise, big production capacity, easy adjustment on the fineness, no dust pollution, easy maintenance and reliable running.

Especially it is used in Silicon smelting magnesium process. Crushing the big rigidity ferrosilicon from 25-40mm to 3-5 mm. Meanwhile, the equipment is also widely used in metallurgical industry, construction industry, land making industry and chemical industry. It is suitable for hardness and middle hardness mineral ore such as iron ore, copper ore, limestone, quartz, granite, sandstone and etc. It will provide perfect material shape outlet. The equipment can meet customers various technical and economical indicator and reach international advanced level.

Ferrosilicon Mill Material is fed into the crusher from inlet port. The material is carried by distributing device.Distributing device make rotational motion with the feeding plate as reference object and put the material into the crushing chamber evenly. The dynamic cone equipped with dynamic toothed plate make rotational motion with the outer cone equipped with static toothed plate as reference object. Material is cut in the crushing chamber shaped between dynamic cone and static cone to fulfill crushing. The crushed material is discharged.

ferrosilicon - an overview | sciencedirect topics

ferrosilicon - an overview | sciencedirect topics

FIGURE 6.14. Round hearth 63 MVA power furnace: 1, mechanism of furnace rotation; 2, furnace shell; 3, arc furnace; 4, feeding funnel; 5, short net; 6, short net flexible bus bars; 7, electrode holders; 8, secondary current leads; 9, electrode contacts; 10, pressure ring; 11, furnace hood; 12, suspension; 13, refractory lining; 14, tap hole.

The silica source for producing ferrosilicon is usually quartzites of lump size 20 to 80 mm, subjected to prewashing, crushing, and grading if needed. Quartzites suitable for smelting of ferrosilicon must contain not less than 97% SiO2 and not more than 1.5% Al2O3. The carbon reductant is usually nut-coke of 5 to 20 mm in size, but as mentioned previously, different producers may have their own local reductant recipes. The reductant should possess high electrical resistance and high reactivity in relation to SiO2 and SiO reduction, and constant moisture content (Batra, 2003). Approximate charge composition, energy demand, and silicon yield for ferrosilicon smelting in closed furnaces are shown in Table 6.7 (Gasik et al., 2011).

The presence of iron during the carbothermic reduction of quartzite lowers the partial pressure of SiO required for reduction to silicon and reduces its activity due to the formation of Fe-Si solutions. Thus, the losses of SiO from the furnace top decrease as the iron content of ferrosilicon increases, so it is typical to have silicon recovery of greater than 90% to 95% for <50% Si grades of ferrosilicon (Vishu et al., 2005).

Ferrosilicon production is a nearly slag-free process (the silicate-based slag amount does not exceed 3% to 5% of the alloy mass). However, the tapping of ferrosilicon and slag through one tap hole might be complicated by changes in the slag composition. The slag is heterogeneous, consisting of silicate-based melts (48% to 50% SiO2, 20% to 25% Al2O3, 15% to 18% CaO), suspension of silicon carbide (10% to 15%), and the metallic inclusions of ferrosilicon alloy. Silicate component is formed from silica and impurity oxides (Al2O3, CaO, MgO) contained in quartzite and coke ash. Silicon carbide forms as an intermediate product of silica reduction by carbon, as shown earlier. Depending on the silicate melt chemical composition, the slag can be solidified in different concentration fields of anorthite (CaOAl2O32SiO2, melting point 1553C) and gehlenite (2CaOAl2O3SiO2, melting point 1545C) of the CaO-Al2O3-SiO2 system (Fig. 6.15).

Anorthite-area compositions, including the presence of SiC particles, have higher viscosity and a lower ability to separate from metal. Therefore, lime is periodically added to increase basicity and to move slag composition into the gehlenite area.

Ringdalen and Tangstad (2012) reported the results of the excavation of an industrial ferrosilicon furnace (Fig. 6.16). They confirmed the existence of one large cavity around each electrode with walls made up of SiC and small amounts of quartz. Several gas channels existed within the walls, creating a layered structure. The channels started at the bottom of the crater, where they were widest. The gas flow appeared to move from the bottom of the crater, through the channels, up to the charge material.

Condensate occurred both in vertical layers outside the crater walls and in a horizontal layer high up through the furnace. Lumpy silica was found only in the upper 20 cm of the charge mixture and below this, the silica component was generally disintegrated. Most of the silica phase was transformed from quartz to cristobalite (Ringdalen and Tangstad, 2012).

Silicon, ferrosilicon and other silicon alloys are produced by reducing quartz, with coal and iron or other ores at very high temperatures (2000C) in electric arc furnaces.385 Some silicon gas (or fume) is produced in the process and reaches the top of the furnace with other combustion gases, where it becomes oxidised to silica by the air and then condenses as submicroscopic particles and agglomerated particles (0.10.5 m) of amorphous silica. This material is usually known as condensed silica fume (csf) or microsilica, and consists of an ultrafine silica (8596 per cent) powder between 50 and 100 times finer than cement or pfa.386

Microsilica for use in concrete derives from the manufacture of ferrosilicon alloys and is processed into micropellets or slurries to facilitate handling. World supplies of microsilica are limited with total production probably being between 1 and 1.5 million tonnes, 80 per cent of which is produced in USA, USSR, Norway and Japan.387 The UK currently imports modest quantities of microsilica for use in concrete. In Iceland blended microsilica-cement is used routinely as a precaution against ASR.388

The potential benefits of using microsilica either as a cement replacement material or as an addition to improve concrete properties have been reviewed by Malhotra and Carette,387 Sellevold and Nilsen389 and Durning and Hicks.390 The disadvantages of using microsilica would probably include the health hazards involved with fine dust materials and the increased cost of the concrete. It has also become apparent that microsilica is typically incompletely dispersed, so that the formation of agglomerates causes the mean particle size to be in the range 150 m, rather than the 0.10.2 m range frequently cited.391 Exceptionally coarse agglomerations of microsilica have the potential to behave as alkali-silica reactive aggregate particles and examples of resultant damage to concrete have been reported.392

The 50% and 75% ferrosilicon (FeSi50 and FeSi75) alloys are produced by carbothermic reduction in a submerged arc furnace. The source of iron is either iron ores or scrap and that for silicon is quartz or quartzite. The principal smelting reaction is the same as that for smelting of metallurgical grade silicon metal (Schei et al. 1998).

The smelting reaction between silica and carbon is characterized by the formation of silicon carbide and SiO gas as intermediary products. Silicon carbide reacts with SiO2 at smelting temperature to form Si and SiO. SiO gas transports to a lower temperature region in the furnace and reacts with carbon and silicon carbide. Unreacted SiO gas escapes to the top of the furnace charge and constitutes a loss of a silicon unit. In smelting 50% and 75% ferrosilicon alloys, iron lowers the activity of silicon, and this reduces the generation of SiO gas. Therefore, the recovery of silicon is higher in 75% and 50% ferrosilicon alloys than in metallurgical grade silicon metal.

The resistance of the charge in smelting ferrosilicon is considerably more than that obtained in ferromanganese operations. This means that higher voltages can be used, permitting the operation of larger furnaces.

As is well known, high silicon-containing alloys do not absorb carbon to any appreciable extent, so that carbon is the natural refractory material for the hearth and the lower side walls of silicon alloy smelting furnaces. The rest of the furnace is generally lined with a high-grade firebrick. The carbon lining can be of prebaked carbon blocks or can be of carbon paste carefully rammed and baked in. At smelting temperatures of the order of 19732073K, these alloys are extremely fluid and it is important to ensure a liquid tight bottom.

Furnaces used for the smelting of high-silicon alloys, i.e., over 70% Si, are mostly of the open-top type, and the carbon monoxide generated is burnt on the top of the furnace. Recently attempts to recover this gas and to close the top of the furnace have been intensified both from emissions and energy recovery points of view. The main problem with respect to closing the top of the furnace was the fact that direct accessibility to the charge from the top was necessary from time to time for poking the charge material to keep it porous and to break up the crust formations.

The same operating principles apply to the smelting of silicon metal as to ferrosilicon, but it is a much more difficult product to make because there is no iron to collect the reduced silicon. The carbon control must be more stringently applied because an error of over- or under-coking is more difficult to correct. It should also be mentioned that the overall recovery of silicon is lower around a maximum of 80%, compared with say 75% ferrosilicon practice where it is commonly around 90%.

The manufacturing processes of silicon metal and ferrosilicon alloys in an electric arc furnace occur at temperatures up to 2000C. They generate fumes containing spherical microparticles of amorphous silicon dioxide. This is the reason why the product is called silica fume or, owing to its form and chemical composition, microsilica, condensed silica fume and volatilised silica.100

The reduction of quartz to silicon releases gaseous SiO. This is transported by combustion gases to lower-temperature zones where it is oxidised by air and condenses in the form of tiny particles of silicon dioxide.

The main features of microsilica are a high silica content, high specific surface area and amorphous structure. These characteristics account for the substantial pozzolanic activity of microsilica, in terms of both its capacity of binding lime and rate of reaction. The chemical composition of microsilica varies with the type of alloy produced within the ranges shown in Table 10.13.101 The silicon metal process gives purer products whereas the production of silicon alloy results in more complex compositions, the minor element content being as high as 30 per cent.102

Microsilica particles are spherical and have an average diameter of 0.1 m. The BET specific surface ranges from 15 to 25 m2/g, with typical values of 20 m2/g.101 Microsilica may contain traces of quartz.93 Low-lime silica fume shows a high degree of condensation of silicate ions since it is formed only by polymeric species.93

This method is based on the use of ferrosilicon as a reductant, giving the overall reaction (CaO)+[Si]FeSi[CaSi2+Si+FeSi2]+(2CaOSiO2). Because the chemical affinity of silicon for oxygen is lower than that of calcium, the reaction can proceed in the direction of obtaining calciumsilicon only in the case of a substantial reduction of the activity of calcium. This specifies high silicon and lower calcium content in the final alloy. Reaction equilibrium is achieved at relatively low concentrations of calcium, so the method can be used to obtain lower grades of calciumsilicon (referred to as FeSiCa) with calcium at less than 20%.

The calciumsilicon smelting is carried out in open furnaces as a batch process. The typical composition of the charge has 200 kg lime, 196 kg ferrosilicon (Fe-75% Si), and 30 kg fluorspar (CaF2). The use of fluorspar is necessary to reduce viscosity of the highly basic slag and to improve conditions for the separation of melt products from the slag. The recovery of calcium is only 20% to 30% (calcium also partially vaporizes) and the utilization of silicon from the ferrosilicon is about 75% to 85%. From the charge materials, into the alloy are transferring approximately 25% to 35% Al, 15% to 30% S, 15% to 35% P, and 25% to 30% Mg. The actual chemical composition of FeSiCa is (% wt.) 15 to 19 Ca, 55 to 65 Si, 18 to 22 Fe, <1 Al, <0.01 S, <0.02 P, and <0.07 C.

The quality of FeSiCa made by silicon reduction is higher than that resulting from carbon reduction, especially in respect of sulfur and carbon contents. Comparative technical and economic indicators of the smelting of calciumsilicon by carbon and silicon reduction are given in Table 19.1. Calciumsilicon alloy is normally supplied to steel mills in different sizes (<2, 2 to 5, 5 to 20, and 20 to 200 mm lumps). Fine sizes of the alloy are not very efficient for steel deoxidation due to significant losses of calcium (low density and high activity with respect to atmospheric oxygen and oxides of the ladle slags). Better use of calciumsilicon is achieved when it is applied in the form of cored wire.

In the Pidgeon process, briquettes of the reactants are prepared and loaded in amounts of around 150kg each into a number of tubular steel retorts that are typically 250300mm in diameter and 3m long. The retorts are then evacuated to a pressure of below 0.1torr and externally heated to a temperature in the range 11501200C, usually by burning coal. Magnesium forms as a vapor that condenses on removable water-cooled sleeves at the ends of the retorts that are located outside the furnace. Approximately 1.1 tonnes of ferrosilicon is consumed for each tonne of magnesium that is produced. Advantages of the Pidgeon process are the relatively low capital cost and the less stringent requirement that is placed on the purity of the raw materials. Major deficiencies are that it is a labor-intensive, batch process which usually only produces about 20kg of magnesium from each retort, and requires a lengthy cycle time of around 8h. The retorts must then be emptied, cleaned, and recharged in conditions that may be dusty and unpleasant. The Pidgeon process has been widely adopted in China where labor costs are low relative to Western nations, and there are readily available supplies of low-cost ferrosilicon and anthracite. Many hundreds of plants of varying sizes have been constructed which, in 2014, supplied about 80% of the worlds magnesium.

The Magntherm process employs an electric arc furnace operating at around 1550C and with an internal pressure of 1015torr. Because the reaction takes place in the liquid phase, the time required for its completion is less than that needed for the Pidgeon process. The furnace may be charged continuously and discharged at regular intervals, and alumina or bauxite is added to the dolomite/ferrosilicon charge which keeps the reaction product, dicalcium silicate, molten so that it can be tapped as a slag. Magnesium is again produced as a vapor which is solidified in an external condenser. Batch sizes may be as high as 11,000kg and plants have operated in France, Japan, the United States, and in the former Yugoslavia.

Alternative thermic techniques have been proposed, although none is currently operating commercially. One idea was to use a plasma arc furnace in which pelletized MgO and coke are fed into a premelted MgO, CaO, Al2O3 slag. The high energy density of the plasma, and the fact that high temperatures (e.g., 1500C) are generated at the surface of the slag where the silicothermic reaction occurs, allows it to be sustained at normal atmospheric pressure. This advantage, combined with the efficient and near total silicon consumption, was claimed to enhance economic competitiveness of the thermic route to magnesium production. However, this development also occurred before use of the Pidgeon process was adopted and greatly expanded in China.

In 2014, one-third of the worlds magnesium was consumed as an alloying element in aluminium and nearly another third was used to desulfurize steels (11%), refine titanium sponge (11%), or produce nodular cast irons (6%). As mentioned earlier, the residual one-third was mainly used to produce lightweight die castings for the automotive industry.

Silica fume is a finely divided by-product material collected from the manufacturing of silicon or ferrosilicon alloys in an electric arc furnace. The residue, carried by the exhaust gas from the furnace as oxidized vapor is air cooled and collected in a form of condensed silica. It is a pozzolanic material with a spherical shape and average particles size less than 0.1m (Fig. 11.3). Condensed silica fume is mainly silicon dioxide made of very fine particles with a typical surface area of about 20,000m2/kg. Table 11.3 shows typical chemical composition of silica fume.

In this process, vanadium slag and silica are used as raw materials, coke is the reducing agent, ferrosilicon is the reducing agent, and lime is the fluxing agent. Ferrosiliconvanadium alloys can be produced by smelting in an electric arc furnace. By controlling the amount of carbonaceous reductant, ferrosiliconvanadium alloy compositions are produced, as shown in Table 10.7. If silicon iron is used as reducing agent, the content of C in the siliconvanadium alloy is <0.5%. The reaction principle is the same as that for ferrovanadium.

In the arc, SiO vapor is formed, but as soon as it leaves the electric arc and comes into contact with oxygen in the air, it is transformed into very fine spherical particles of SiO2 (to minimize their superficial energy) that contain more than 85% of vitreous silica.

When the furnace is equipped with a heat recovery system, the silica fume particles collected in the de-dusting system are whitish, because they leave the furnace at a temperature of about 800C, which is sufficiently high to burn all the traces of carbon.

When the furnace is not equipped with a heat recovery system, the silica fume particles collected in the de-dusting system have a gray color, because they left the furnace at temperature lower than 200C after being mixed with fresh air to cool down the hotfurnace gases, so they do not burn the de-dusting sacks used to collect them (Figure 4.13b).

After reheating, the silica crystallizes as cristobalite. The hump found in the as-produced silica fume corresponds to the main pick of cristobalite, which indicates than in a silica fume particle, silica tetrahedrons are organized as in cristobalite on a short-range distance.

Figure4.15. Silica fume as seen under an electronic microscope: (a)scanning electronic microscope silica fume particles are naturally agglomerated in an as-produced silica fume. (b)Transmission electronic microscope dispersed individual particles.

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